A wireless local area network (WLAN for short) is a network system in which data is transmitted over the air using a radio frequency technology. With wide application of smart terminals, people have a growing demand for data network traffic, and using a WLAN to carry the traffic has become one of very important information data transmission manners.
A WLAN technology cannot develop without formulation and widespread application of WLAN standards. The Institute of Electrical and Electronics Engineers (IEEE for short) 802.11 family are main WLAN standards, and include several generations of prevailing standards: 802.11, 802.11b/g/a, 802.11n, and 802.11ac.
The WLAN technology is based on a computer network and a wireless communications technology. In a computer network structure, a logical link control (LLC) layer and an application layer above the logical link control layer may have same or different requirements on different physical (PHY) layers. Therefore, the WLAN standards are mainly directed at a physical layer and a Media Access Control (MAC) layer, and involve technical specifications and technical standards such as a range of used wireless frequencies, an air interface communications protocol, and the like.
A physical layer frame in the WLAN standards is also referred to as a physical layer convergence procedure (PLCP) protocol data unit (PPDU), and includes a PLCP header field and a PLCP service data unit (PSDU). The PLCP Header mainly includes a training field and a signal (SIG) field. The PSDU includes a MAC header field and a MAC service data unit.
Currently, the 802.11ax standard (also referred to as a high efficiency wireless local area network, High Efficiency WLAN (HEW) standard) under study and formulation further evolves the WLAN technology. In the 802.11ax standard, orthogonal frequency division multiple access (OFDMA) will be used as one of main technical points to improve transmission efficiency.
Currently, based on a design of signaling for an 802.11ax system, the signaling includes first high-efficiency signaling (HE-SIG-A) and second high-efficiency signaling (HE-SIG-B). The first high-efficiency signaling includes SU/MU indication information and UL/DL indication information. The SU/MU indication information is used to indicate whether a transmission type of subsequent data of the first high-efficiency signaling is single-user transmission or multi-user transmission. When the transmission type is only the SU transmission, HE-SIG-A includes UL/DL indication information, where the indication information is used to indicate whether a type of the current data packet transmission is uplink transmission or downlink transmission.
Currently, a MAC frame header based on an 802.11 system includes fields such as a frame control field, and a transmitter address (TA) and a receiver address (RA) of a data packet. The frame control field includes a To DS field and a From DS field, where the To DS field and the From DS field are used to describe whether a data packet comes from a distributed system and whether a data packet goes to the distributed system. The distributed system herein is a system that is used to connect multiple basic service sets (BSSs) and integrate multiple local area networks to create an extended service set (A system used to interconnect a set of basic service sets (BSSs) and integrated local area networks (LANs) to create an extended service set (ESS)).
In the 11ax system, when the SU/MU indication in HE-SIG-A is SU, HE-SIG-A includes a UL/DL field. The indication field is used to describe whether a transmission direction of the PPDU is uplink (UL) (e.g., from a STA to an AP) or downlink (DL) (e.g., from an AP to a STA). Direct communication between stations is an important communication manner of the 802.11 WLAN system. Data transmission between stations is implemented by means of direct transmission rather than by using an AP. The direct communication between stations is neither uplink nor downlink. When Device-to-Device (D2D) data transmission is performed, the UL/DL indication field in HE-SIG-A does not have information used to indicate uplink or downlink.